United States Forces-Iraq (USFI), the American military command in Iraq, cased its colors Thursday outside Baghdad International Airport (BIAP). During the traditional military ceremony, the unitâ€™s colors were rolled and stowed, symbolizing the disestablishment of the formation and the end of the U.S. militaryâ€™s nondiplomatic presence in the country. The last U.S. forces (save a company-sized Marine Security Guard detachment at the U.S. Embassy) are slated to leave the country next week, well ahead of the Dec. 31 deadline stipulated by the status of forces agreement between Washington and Baghdad.

In April 2003, then-Saddam International Airport was designated Objective Lions and seized by Task Force 2-7 in an assault for which an Army combat engineer would posthumously receive the Medal of Honor. These were the days of â€śshock and awe,â€ť as the outset of the war in Iraq was dubbed, during which the United States military occupied the Iraqi capital in a matter of weeks. Objective Lions would quickly become the sprawling Victory Base Complex, the iconic centerpiece of the United Statesâ€™ eight-year war in Iraq. Two American presidents would subsequently pass through BIAP, the center of the operation that became the focal point of U.S. military operations and foreign policy for the better part of a decade.

In invading Iraq, the United States had hoped to fundamentally reshape the regionâ€™s geopolitical reality by establishing a pro-American regime in Baghdad. The invasion did reshape the region, but not in the way Washington had intended. The invasion and subsequent American pressure did ultimately push Saudi Arabia to cooperate with Washingtonâ€™s counterterrorism objectives, as well as prompt Riyadh to begin meaningfully, and with increased aggression, confronting the radical Islamist elements within its own borders. But the fall of Saddam Husseinâ€™s regime also destroyed the established balance of power between Iran and Iraq, which had stood as a pillar of American foreign policy in the region for generations.

As the American war effort deteriorated into a protracted counterinsurgency and nation-building project, resurgent Iranian influence and power became increasingly difficult to ignore. The United States and its allies found themselves fighting not only foreign jihadists but domestic Sunni nationalists and Shiite militias, some armed with improvised explosive devices provided by Iran â€” the single most deadly and effective weapons used to kill U.S. and allied troops.

The war ultimately cost the lives of almost 4,500 American troops, more than 300 allied troops, and a likely unknowable number of Iraqis. The United States maintained more than 100,000 troops on the ground in Iraq â€” and for a significant period closer to 200,000 â€” throughout almost the entire duration of the war. That number does not count significant contributions made by allies, not to mention the legions of private security contractors that supplemented those forces. While this was never sufficient to impose a military reality on the country â€” the numbers, in other words, were not substantial enough to pacify the population â€” this nevertheless represented an enormous and sustained commitment. It impacted the entire power structure in Iraq, the balance of power in the region and American military commitments elsewhere in the world. The structural significance of this commitment of forces is difficult to overstate, therefore it is difficult to overstate the significance of that forceâ€™s removal.

Only a few thousand American troops remain in the country, and for all practical purposes, USFI has long been declining as a significant military presence. But few elements operating in Iraq or Iran had any interest in taking any action that might delay the U.S. withdrawal. When USFI finally leaves next week, it is hard to envision a force of any magnitude being redeployed to the country in the foreseeable future â€” barring an extreme scenario â€” for any length of time. The circumstance most likely to lead U.S. troops to intervene would probably involve a noncombatant evacuation of diplomatic personnel and American nationals (for the purposes of that evacuation, the runway at BIAP will likely play a central role in American thinking about Iraq.)

In short, a key structural element of the framework in which Iraq and the wider region has operated for nearly a decade officially ceased to exist on Thursday. And this framework played a central role in the apparent quietude of Iraq in recent years. That quietude cannot be taken for granted moving forward, and the most important geopolitical result of the American invasion of Iraq â€” the emergence of Iran as a regional power â€” has yet to be meaningfully addressed and countered.